Apparatus for printing three-dimensional (3D) objects

ABSTRACT

A method of printing a three-dimensional (3D) object and a support construction for the 3D object includes depositing a model material, layer-by-layer, on a fabrication platform, to print a first portion of the 3D object, and depositing a support material, layer-by-layer on the fabrication platform, to print the support construction, wherein, in a predetermined number of the deposited layers, the model material and the support material are deposited such that a gap is formed between a surface of the first portion of the 3D object and a surface of the support construction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. Pat. No. 11,020,896, filedAug. 20, 2019, which is a Continuation of U.S. Pat. No. 10,427,354,filed Dec. 6, 2017, which is a U.S. National Stage of InternationalApplication No. PCT/IL/2016/050587, filed Jun. 7, 2016, which claims thebenefit of U.S. Provisional Application No. 62/172,096, filed on Jun. 7,2015.

BACKGROUND

In three-dimensional (3D) printing or 3D fabrication process, materialis selectively jetted from one or more print heads and deposited onto afabrication tray in consecutive layers according to a pre-determinedconfiguration as defined by a software file. Some deposition processesinclude depositing different materials in order to form a single objector model. For example, an object may be deposited using a first materialfor depositing the body structure and a second material for depositing asupport structure to support various sections of the body structure, forexample, negative angle surfaces and overhangs. The support material islater being removed by mechanical, chemical or other means to reveal thefinal object.

Conventional deposition methods involve depositing the support materialand the body material simultaneously layer by layer, according to thepre-determined configuration. Both the support material and the bodymaterial are deposited in a liquid or semi liquid state in the samelayer, such that a liquid/liquid interface is formed between the twomaterials. After the deposition the deposited layers are hardened (e.g.,by ultraviolet (UV) curing). The droplets of body material and supportmaterial create a mix layer and upon removal of the support materialmicro-cracks are left in the printed part (i.e. body material). Thesurface micro-cracks may lead to an increased stress under load and anincreased brittleness of the printed parts. The rougher the surface thepoorer the mechanical strength of the printed model.

SUMMARY

Some embodiments of the invention may be directed to a system and methodof printing a three-dimensional (3D) object and a support constructionfor the 3D object. The system may include a printing unit comprising oneor more print heads configured to deposit body material for forming the3D object and support material for forming the support construction anda supply system for supplying the body material and support material tothe printing unit. The system may further include a controller toexecute methods according to some embodiments of the invention.

The controller may be configured to generate 3D cross sectional digitaldata comprising a set of horizontal slices, wherein each of the slicesincludes one or more body regions representing a horizontal crosssection of the 3D object, and at least each of some of the slicesfurther includes one or more support regions being adjacent to the bodyregion and representing a corresponding horizontal cross section of thesupport construction.

The controller may further be configured to manipulate the 3D digitaldata to create a set of shifted slices by performing vertical shiftsbetween the body region and the support region of a same horizontalslice to create printing digital data, wherein at least each of some ofthe shifted slices includes a body region of one of the horizontalslices together with a support region of another one of the horizontalslices; and controlling the printing unit to deposit, in layers, fromthe one or more printing heads, the body material and the supportmaterial based on the printing digital data, wherein in a single scan,droplets of the support material and droplets of the body materialtravel different distances.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 is a diagrammatic representation of a printing system accordingto some embodiments of the invention;

FIG. 2 is a flowchart of a method of printing a three-dimensional (3D)object and a support construction for the 3D object according to someembodiments of the invention;

FIGS. 3A-3B are graphical representations of exemplary cross sectionaldigital data of an object and support construction according to someembodiments of the invention;

FIG. 4 is a graphical representation of exemplary cross sectional dataof an object and support construction according to some embodiments ofthe invention;

FIG. 5 is a graphical representation of exemplary cross sectionaldigital data of an object and support construction according to someembodiments of the invention;

FIGS. 6A-6C are graphical representations of exemplary cross sectionaldata of objects and support constructions according to some embodimentsof the invention;

FIG. 7A is an image of an exemplary printed object according to someembodiments of the invention; and

FIG. 7B depicts a cross section of the exemplary printed object of FIG.7A and a graph that matches the surface curvature of the printed objectaccording to some embodiments of the invention;

FIGS. 8A and 8B are exemplary printed objects according to someembodiments of the invention;

FIG. 9 depicts exemplary support structures according to someembodiments of the invention;

FIG. 10 includes depictions of exemplary printed objects according tosome embodiments of the invention;

FIGS. 11A and 11B are exemplary printed objects according to someembodiments of the invention.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

Embodiments of the invention may be directed to printing 3D models usingink-jet printing system. In order to print complex shapes, supportmaterial is deposited at desired areas to support the body materialduring the construction of the model. When the support material and bodymaterial are printed together in the same layer, a mixed interfacecomprising support material droplets and body material droplets isformed. After hardening of the printed layers, the interface formedbetween the support material and the body material is rough. Therefore,upon removal of the support material and revealing of the bodystructure, the surface of the body would also be rough and full ofmicro-cracks, which leads to a reduced mechanical strength and inferiormechanical properties.

In the common practice, droplets of body material and support materialdeposited together during a single scan may create a mixed interface andupon removing of the support material micro-cracks are left in theprinted body part. The surface micro-cracks may lead to increasedmicro-stresses once under load and increased brittleness of the printedparts. The outcome of the common practice printing methods has inferiormechanical properties and finer (e.g., smoother) surface roughness.

In addition to the brittleness problem, irregular morphology of theresulting matte surfaces (i.e. rough surface as oppose to glossysurface) may cause the following problems: part distortion, loweraccuracy, lower dimensional stability, higher water absorption,increased creep, non-uniform appearance and other undesirable opticaleffects. At least some of the above problems may be resolved byexpensive and time consuming post-processing, such as sanding, polishingand lacquering.

Surface cracks may be caused by an overlap and/or intermixing betweenbody material and support material droplets. Therefore, the preventionof direct contact between the support and modeling materials mayeliminate the afore-mentioned problems. In some embodiments, the 3Dprinting process is modified and a delay is introduced between thedeposition of the body materials and the support material. Such aprocess significantly improves the performance and appearance of thefinal printed part/s or object/s.

Free surfaces of a model or support materials that have been depositedwithout any mixed interface with another material may be smoother andhave better mechanical properties. Occasionally, solid/solid interfacesand solid/liquid interfaces deposited in a layer by layer manner mayresult in coarse interface (mixed interface) having poorer mechanicalproperties.

Embodiments of the invention may be related to a system and method forprinting a 3D object supported by a support construction such thatsubstantially, no mixed interface is formed between a body material(forming the 3D object) and a support material (forming the supportconstruction). A 3D object printed according to embodiments of theinvention may have a smoother surface with less micro-cracks and bettermechanical properties. A 3D digital data of the 3D object and thesupport construction may be generated to include horizontal slicescomprising one or more body regions representing a horizontal crosssection of the 3D object and optionally also one or more support regionsbeing adjacent to the body region and representing a correspondinghorizontal cross section of the support construction.

The 3D digital data may further be manipulated to create a set ofshifted slices by performing vertical shifts between the body region andthe support region to separate during printing the body regions from thesupport regions. In some embodiments, when printing the 3D object andthe support structure according to the manipulated 3D digital data in asingle scan, droplets of the support material and droplets of the bodymaterial may travel different distances. In a single scan, the bodymaterial may be deposited to form a first horizontal slice of a firstheight and the support material may be deposited to form a secondhorizontal slice being at a second height. In some embodiments, thesecond height may be higher than the first height by the vertical shift.

Reference is made to FIG. 1 presenting a diagrammatic representation ofa system for depositing 3D objects according to some embodiments of theinvention. A system 10 may include a printing unit 20, a supply system30, a controller 40, a user interface 50 and a fabrication platform or atray 60. Controller 40 may be configured to control all the otherelements of system 10.

Printing unit 20 may include one or more print heads 22, for example,heads 1-n, one or more hardening devices 24, and one or more levelingdevices 26. Print heads 22 may be configured to deposit material usingany ink-jet method. Printing unit 20 may move horizontally in both X andY directions and vertically in the Z direction.

Print heads 22 may include an array of two or more nozzles arranged, forexample, in a single line or in a 2D array. Different print heads 22 maydeposit different material such that two or more materials may bedeposited at a single deposition scan. For example, print heads 1 and 2may be configured to print support material and print heads 3 and 4 maybe configured to print body material. Print heads 22 may be fed (withthe deposition material) from supply system 30.

Hardening device 24 may include any device that is configured to emitlight, heat and the like that may cause the printed material tohardened. For example, hardening device 24 may include one or moreultraviolet (UV) lamps for curing the deposited material. Levelingdevice 26 may include any device that is configured to level and/orestablish a thickness of the newly formed layer by sweeping over thelayer and removing excess material. For example, leveling device 26 maybe a roller. Leveling device 24 may include a waste collection device(not illustrated) for collecting the excess material generated duringleveling.

Supply system 30 may include two or more building material containers orcartridges for supplying a plurality of building materials to printheads 22. In some embodiments, the body material may be formed by mixingtwo or more base materials prior to the deposition of the body materialfrom print heads 22. Each of the base materials may be held in adifferent container included in supply system 30. The two or more basematerials may be mixed in an additional container prior to the feedingof print head 22 or may be fed together to print head 22 and mixedtogether during the deposition processes. Alternatively, each of the twoor more base materials may be deposited from a different print head 22at a single place (e.g., a plurality of droplets of different basematerials may be deposited on the same spot) and mixed together afterthe deposition. A similar process may be implemented with respect to thematerial(s) forming the support construction, when the support materialincludes mixing of one or more base materials. The mixing process of thetwo or more based materials and other aspects of the material supplyfrom supplying system 30 to print heads 22 may be controlled bycontroller 40.

Controller 40 may include a processor 42 that may be, for example, acentral processing unit processor (CPU), a chip or any suitablecomputing or computational device. Controller 40 may further include: amemory 44 and storage unit 46. For example, processor 42 may control themovement of printing unit 20 at a desired direction. Memory 44 mayinclude for example, a Random Access Memory (RAM), a read only memory(ROM), a Dynamic RAM (DRAM), a Synchronous DRAM (SD-RAM), a double datarate (DDR) memory chip, a Flash memory, a volatile memory, anon-volatile memory, a cache memory, a buffer, a short term memory unit,a long term memory unit, or other suitable memory units or storageunits. Memory 44 may be or may include a plurality of possibly differentmemory units.

Memory 44 may include an executable code, e.g., an application, aprogram, a process, task or script. The executable code may includecodes or instructions for controlling apparatus 10 to print 3D objectsaccording to embodiments of the present invention. For example, memory44 may include a code for depositing support material to form a firstregion of the 3D object, using for example, a first set of print heads22, and harden the material in the first region using, for example,hardening device 24. The code may further include depositing bodymaterial in a second region of the 3D object horizontally adjacent tothe first only after the material in the first region was hardened.

In some embodiments, memory 44 may include instruction to generate 3Dcross sectional digital data comprising a set of horizontal slices. Theinstructions may further include depositing the body and supportmaterials based on 3D digital data, such that, at least some of theslices are combined slices that include both a support region to beprinted by the support material and a body region to be printed by thebody material. The 3D digital data corresponding to cross section slicesof the 3D object and the support structure may be stored in storage unit46.

Storage unit 46 may store files that include design parameters of the 3Dobjects and the corresponding support structures to be printed byapparatus 10. For example, 3D computer aided design (CAD) files thatinclude the design of the 3D object may be stored in storage unit 46.The files may include the dimensions and locations of the differentregions of the 3D objects and the corresponding regions of the supportconstruction.

Apparatus 10 may further include a user interface 50. User interface 50may be or may include input devices such as, a mouse, a keyboard, atouch screen or pad or any suitable input device. It will be recognizedthat any suitable number of input devices may be included in userinterface 50. User interface 50 may further include output devices suchas: one or more displays, speakers and/or any other suitable outputdevices. It will be recognized that any suitable number of outputdevices may be included in user interface 50. Any applicableinput/output (I/O) devices may be connected to controller 40 as shown byblock 50. For example, a wired or wireless network interface card (NIC),a modem, printer or facsimile machine, a universal serial bus (USB)device or external hard drive may be included in user interface 50. Userinterface 50 may allow a user to upload or update codes and instructionsfor controlling printing of 3D objects according to some embodiments ofthe invention and/or to upload and updates files comprising the designof the 3D objects (e.g., computer aided design (CAD) files) into storageunit 46.

Tray 60 may be any tray that is suitable to support ink-jet printing of3D objects and the corresponding support constructions. Tray 60 may beattached or connected to an X-Y table and may be controlled, e.g., bycontroller 40, to move in the X-Y plan according to the requirements ofthe printing process. Additionally or alternatively, tray 60 may beconfigured to move in the Z direction.

Controller 40 may control printing unit 20 and/or tray 60 to cause arelative movement between the tray and print heads 22, such that each ofprint heads 22 may deposit droplets of printing material (e.g., body orsupport materials) at a predetermined location in the X-Y plan and at apredetermined height at the Z direction.

Reference is made to FIG. 2 which is a flowchart of a method of printinga 3D object and a support construction for the 3D object according tosome embodiments of the invention. The method of FIG. 2 may be performedby a system such as system 10 or by any other suitable system. A 3Dcross sectional digital data comprising a set of horizontal slices maybe generated (Box 210), for example, by controller 40. A graphicalrepresentation of such cross sectional digital data is shown in FIGS. 3Aand 3B. FIGS. 3A and 3B are illustrations of a cut in a 3D digital dataof a 3D object 300 and a support construction 305. The 3D digital datamay include 5 horizontal slices 310-350. As it should be understood byone skilled in the art that the 5 slices illustrated in FIGS. 3A-3B aregiven as an example and the invention is not limited to any number ofslices.

In some embodiments, each of slices 310-350 includes one or more bodyregions 314-354 representing a horizontal cross section of 3D object300, and at least each of some of the slices may further include one ormore support regions 312-352 being adjacent to body regions 314-354 andrepresenting a corresponding horizontal cross section of supportconstruction 305. For example, slice 310 may include a support region312 and a body region 314. In some embodiments, each slice includes oneor more deposition layers, for example, two or more deposition layers.

Referring back to FIG. 2 , the 3D cross sectional digital data may bemanipulated, for example, by controller 40, to create a set of shiftedslices 310 a-350 a (shown in FIG. 3B) by performing vertical shifts 360between body region 314-354 and the support region 312-352 of a samehorizontal slice (box 220). Shifted slices 310 a-350 a may create aprinting digital data such that at least each of some of the shiftedslices include a body region of one of the horizontal slices togetherwith a support region of another one of the horizontal slice. Forexample, shifted slice 320 a may include a body region 324 includedoriginally in horizontal slice 320 and support region 332 includedoriginally in horizontal slice 330.

In some embodiments, the method includes determining a size of verticalshift 360 (also referred to as “Z-gap”) between body regions 314-354 andsupport regions 312-352 based on a geometrical relationship between 3Dobject 300 and support construction 305. For example, the geometricalrelationship may be an angle α (illustrated in FIG. 3B) formed between asurface 370 representing the interface between body regions 314-354 andsupport regions 312-352 and the horizontal plan. In some embodiments,the angle α between adjacent body regions and support regions is up to70°. Higher angle α requires a larger vertical shift 360. In anotherexample, the geometrical relationship may include radius of curvaturebetween the body regions and the support regions.

In some embodiments, the 3D cross sectional digital data may furtherinclude a set of vertical columns 661-671, as illustrated and discussedin details with respect to FIG. 5 . In some embodiments, each of columns661-671 may include one or more slices of body regions 610 representinga vertical column of the 3D object, and at least each of some of thecolumns 661-671 may further include one or more slices of supportregions 630 being vertically adjacent to the body region andrepresenting a corresponding vertical column of the supportconstruction. In some embodiments, manipulating the 3D digital datafurther includes adding to each column 661-671 a delay in the printingprocess between every vertically adjacent body region and supportregion.

Referring back to FIG. 2 , controller 40 may control print heads 22 ofprinting unit 20 to deposit a body material and a support material (Box230). The body material and support material may be deposited based onthe printing digital data created in the operation of Box 220. In someembodiments, during the same deposition scan droplets of the supportmaterial and droplets of the body material travel different distances.For example, in the same deposition scan droplets of support materialmay be deposited to form support region 322 and droplets of bodymaterial may be deposited to form body region 314. The droplets of thebody material may travel a longer distance from print head 22 than thedroplets of the support material. The droplets of the body material maytravel an extra distance equal to the “vertical shift” 360 untilreaching their final position.

In some embodiments, the method further includes hardening the depositedbody material and the deposited support material after at least some ofthe scans. For example, one or more hardening devices 24 may harden thedeposited droplets after every scan (every deposited layer), or afterthe deposition of an entire slice, when the slice includes more than onedeposition layer. In some embodiments, each scan may include depositinga single layer. In some embodiments, prior to depositing an additionalslice, the entire deposited material may be hardened, to avoid forming amixed interface between the support and body materials.

A printing sequence according to some embodiments of the invention maybe better understood in accordance to the graphical representation ofthe 3D cross sectional digital data in FIG. 4 . An exemplary 3D crosssectional digital data of an object 400 may include a set of horizontalslices comprising a corresponding plurality of body regions 401-409forming together, for example, an “I” shape 3D object and a plurality ofsupport regions 421-427 forming together the support construction forthe “I” shape 3D object. The size, dimension and location of each regionof the 3D cross sectional digital data may be determined by computersimulation and the results of the simulation may be stored as CAD filesin a storage unit associated with an apparatus for printing 3D objects,for example, storage unit 46 included in apparatus 10.

In some embodiments, object 400 may be printed according to someembodiments of the invention, for example, according to the method ofFIG. 2 . Object 400 may be manufactured using any apparatus that isconfigured to manufacture a 3D object by deposition of material layer bylayer, for example, system 10.

Object 400 may be printed on or may include a base region 420 that mayinclude two or more layers of the support material. The two or morelayers may be deposited on a printing tray (e.g., tray 60) and hardenedprior to printing the “I” shape 3D object.

In some embodiments, a body region 401 may be deposited on top of thehardened region 420. Body region 401 may include one or more layers ofbody material for building the “I” shape 3D object. The layers in region401 may be deposited in a liquid state and may be hardened, for example,by hardening device 24, prior to the deposition of support region 421.Support region 421 may include one or more layers of support material.The material in the layers of support region 421 may be hardened priorto the deposition of body region 402, such that a mixed interfacebetween the body material and the support material is not enabled.Region 402 may be horizontally adjacent to region 421.

In some embodiments, the same scan droplets of support material forforming support region 422 may be deposited on top of support region 421simultaneously to the deposition of droplets of body material formingbody region 402. A vertical shift in the size of the thickness ofregions 421-427 may be formed between body region 402 and support region421. The alternating depositions and hardening process of the regionsmay continue as long as an interface between the body material andsupport material when both in a liquid state or when an overlap betweenbody and support material occur in an alternating manner is not enabled.For example, region 403 may be deposited in the same scan(s) with region423, region 404 in the same scan(s) with region 424, region 405 withregion 425, region 406 with region 426, region 407 with region 427. Thelast two regions to be deposited may be body structure regions 408 and409.

Reference is made to FIG. 5 which is a graphical representation of 3Dcross sectional digital data according to some embodiments of theinvention. The 3D cross sectional digital data may include verticalcolumns comprising a plurality of deposited slices, wherein each columnmay be related to a single deposited spot at each slice. The informationregarding the 3D digital data may include, if at a particular slice, ata particular column, a body material or a support material to bedeposited. Each deposited spot or point may include a single droplet ofink, or may include more than one droplet of ink. For example, model 600may be divided (in the x direction) into 11 columns 661-671. Each ofcolumns 661-671 may include body material slices and/or support materialslices. For example, column 661 may include, from bottom to top: 3support slices 610, 6 body slices 620, 30 support slices 360 and 6 bodyslices 620. In some embodiments, each slice may include a singledeposition layer.

In some embodiments, for each column a number and location of transitionpoints between support material and body material may be determined. Thetransition points may be defined as the points where the printedmaterial changes from support material to body material or vice versa.For example, column 661 has three transition points, 615, 625 and 635where the printed material changes from support material to bodymaterial or vice versa.

The 3D cross sectional digital data may include a 2D matrix of vectorsthat may present the 3D model, where each vector presets a singlecolumn. The vector may include, counting from bottom to top the numberof slices belongs to a first material until a first change in thematerial (i.e., transition point) then counting the number of layers ofthe second material until the second transition point, etc. For example,the vector presenting column 661 may have the form of:

{3-0, 6-1, 30-0, 6-1}

Wherein the first number at each pair of numbers stands for the numberof slices and the second number stands for the material of the slice,for example, 0 for support material and 1 for body material.

An exemplary matrix for the two dimensional model 600 may include thefollowing vectors:

Column 661: {3-0, 6-1, 30-0, 6-1}

Column 662: {3-0, 6-1, 30-0, 6-1}

Column 663: {3-0, 6-1, 30-0, 6-1}

Column 664: {3-0, 6-1, 30-0, 6-1}

Column 665: {3-0, 42-1}

Column 666: {3-0, 42-1}

Column 667: {3-0, 42-1}

Column 668: {3-0, 6-1, 30-0, 6-1}

Column 669: {3-0, 6-1, 30-0, 6-1}

Column 670: {3-0, 6-1, 30-0, 6-1}

Column 671: {3-0, 6-1, 30-0, 6-1}

In some embodiments, a delay in the printing process may be introducedin the transition points as a deposition delay of N printed slices(e.g., layers) at each transition point of each column. The depositiondelay may be applied at each transition point such that after completingthe deposition of the first material, for N deposited slices, nomaterial is deposited at that particular point. For example, thedeposition sequence of column 661, when N=7, may include depositing 3layers of support material and not depositing any material in thefollowing 7 depositions. Meaning that the print head (e.g., print head22) does not drop any material in column 661 for 7 scans and onlyhardening device (e.g., device 24) heats or radiates the supportmaterial deposited 7 times allowing the support material to fully hardenor cure. After the delay, 6 layers of body material may be deposited andanother delay of 7 layers may be applied.

It is to be understood that each scan may include depositing material atdesired places and hardening of each layer. So when the materialdeposition at a particular place (e.g., a column) is avoided only thehardening process is applied at that particular place. For example,after depositing the first 3 layers of support material in region 610,no material is to be deposited at any column and only the hardeningdevice may scan the entire model 7 times.

An exemplary matrix for the two dimensional model 600, that includes adelay of 7 layers represented by the number 2 may include the followingvectors that corresponds to columns 661-671:

{3-0, 7-2, 6-1, 7-2, 30-0, 7-2, 6-1}

{3-0, 7-2, 6-1, 7-2, 30-0, 7-2, 6-1}

{3-0, 7-2, 6-1, 7-2, 30-0, 7-2, 6-1}

{3-0, 7-2, 6-1, 7-2, 30-0, 7-2, 6-1}

{3-0, 7-2, 42-1}

{3-0, 7-2, 42-1}

{3-0, 7-2, 42-1}

{3-0, 7-2, 6-1, 7-2, 30-0, 7-2, 6-1}

{3-0, 7-2, 6-1, 7-2, 30-0, 7-2, 6-1}

{3-0, 7-2, 6-1, 7-2, 30-0, 7-2, 6-1}

{3-0, 7-2, 6-1, 7-2, 30-0, 7-2, 6-1}

In some embodiments, depositing the object layer by layer according tothe determined slices and columns may include applying the delay at eachtransition point by not depositing any material for N layers, whereineach layer is deposited at a single scan. For example, the next 7 layersdeposited after transition point 625 may include, not depositing anymaterial at columns 661-664, depositing body material at columns 665-667and not depositing any material at columns 668-671, hardening the bodymaterial after each layer. The deposition of the 8^(th) layer, abovepoint 625, may include depositing support material at columns 661-664,depositing body material at columns 665-667 and again support materialat columns 668-671, followed by additional curing scans with no furtherdeposition of material in order to fully harden the support materialdeposited. The support material at columns 661-664 and 668-671 may bedropped 7 layers lower than the body material in column 665-667,accordingly, in some embodiments, the delay may be equal to the verticalshift.

Some embodiments of the invention may be related to a roller-lessdeposition process. In some embodiments, material is deposited at atleast two different heights, as illustrated and discussed with respectto FIGS. 2-5 . When depositing together two regions at two differentheights (e.g., at a vertical shift), for example, regions 322 and 314,it may be difficult to level each deposited layer by using a levelingdevice, for example, leveling device 26. In some embodiments, in orderto avoid the deposition of excess material and the need to use theleveling device, not all the droplets included in a layer are deposited.For example, apparatus 10 may deposit droplets of body or supportmaterial only at 80% of the places in which a droplet may be deposited.The not deposited “vacancies” may be filled with material from theexcess material deposited in the 80% places of the layer. The number andlocation of the vacancies may be such that substantially no excessmaterial may be depo sited.

Reference is made to FIGS. 6A-6C that are illustrations of graphicalrepresentations of exemplary cross sectional data of objects and supportconstructions according to some embodiments of the invention. Objects1110, 1120 and 1130 may be deposited using at least two materials (e.g.,body material and a support material) layer by layer. Object 1110 may bedeposited using prior art methods such that at each deposition scan bothfirst material regions 1111 and second material regions 1115 may bedeposited simultaneously at the same height, such that after eachdeposition scan (or every several deposition scans) a leveling devicemay level the deposited layer(s) such that each adjacent regions 1111and 1115 may have the same height.

Object 1120 may be deposited using the deposition methods disclosed inFIG. 2 . The method may include depositing the first bottom region 1111from the first material, leveling and curing each layer and thendepositing the first 1125 region from the second material and secondregion 111 from the second material in the same scans. Since the secondmaterial in region 1125 is deposited below first region 1111, theleveling device cannot level the access second material deposited. Whena droplet is being deposited, it flattens and occupies a larger areathan the diameter of the droplet, such that neighboring depositeddroplets overlap each other, forming excess material in some areas overthe surface. This excess material should be removed in order to maintaina controlled height of each region. When the excess material is notremoved the height of the region cannot be controlled. Therefore, if thedeposition sequence continue without removing the excess material inregions 1125 by the leveling device, each region 1125 may include moredeposited material than in each region 1111 where the excess materialhas been removed by the leveling device, and may be higher than region1111, resulting in an uneven final height of object 1120.

In some embodiments, in order to solve this problem, at least some ofthe second material that was expected to be deposited in each layerforming region 1125 is not deposited and a vacancy (a place where nomaterial is deposited) is “deposited”. The amount of vacancies may becalculated such that no leveling may be needed and the height of atleast some of the regions deposited from the second material may besubstantially similar to the height of the regions deposited using thefirst material.

The amount of material not deposited using the vacancies may besubstantially equal to the amount of excess material that may be removedby the leveling device. For example, if the leveling device removes 15%of the material deposited in a single scan, only 85% of the material maybe deposited in regions where the leveling device may not be in directcontact during the leveling process (due to the Z-gap). In other words,15% of the droplets of the second material that are supposed to bedropped in a single scan are vacancies.

Object 1130 illustrated in FIG. 6C may include two parts deposited fromtwo different materials. Object 1130 may be deposited using the methoddisclosed in FIG. 2 . The left part of object 1130 may include regions1111 deposited by dropping droplets of the first material and the rightpart may include regions 1135 and 1125 deposited by dropping droplets ofthe second material. Following the deposition of any one of regions1111, the leveling device may level the deposited material. The firstregion 1135 of the second material may be deposited after the depositionof at least one region 1111, and therefore cannot be leveled by theleveling device. In order for the final region 1135 to be at the sameheight as region 1111, less material may be deposited in region 1135 incomparison to the corresponding adjacent region 1111.

In some embodiments, at a predetermined number of printing spots atregion 1135, no droplets are being placed and a vacancy is formed. Thevacancies may be filed with material from neighboring droplets beingdeposited. The amount of material to be deposited may be proportional tothe amount of material that was remained in region 1111 after theleveling process. For example, if 80% of the first material that wasdeposited in region 1111 is remained after the leveling process only 80%of the original amount of the second material may be deposited in region1135.

In some embodiments, an alternative approach to reducing the excessmaterial may be taken as illustrated and demonstrated in regions such asregions 1125. In regions 1125 all the material may be deposited (i.e.,no vacancies are introduced into the printing instructions). Theprinting method may include instructions to deposit a predeterminednumber of regions with a reduced amount of material (e.g., regions 1135)and additional predetermined number of regions with full amount ofmaterial (e.g., regions 1125) such that the overall height of alldeposited regions of the second material may not exceed the overallheight of all deposited regions of the first material (that includeregions 1111). The last layer of the second material being depositedmany be leveled using the leveling device.

In some embodiments, the vacancies or placed where no droplets are to bedeposited are located a predetermined areas over the surface of theprinted object. When all the droplets are being deposited and noleveling device levels the deposited droplets, the outcome may be anuneven height of the deposited object or region, as illustrated forexample, in FIG. 7A. FIG. 7A is an exemplary printed object according tosome embodiments of the invention. An amount of excess material may beformed in the side and middle section of the deposited region. When aleveling device levels the deposited material the excess material in thesides and the middle sections may be removed. In order to avoid suchunevenness when not using a leveling device (e.g., when applying themethod of FIG. 2 ), vacancies may be introduced at areas when moresexcess material is to be deposited, such as the sides and the middlesections of the printed region of FIG. 7A.

In some embodiments, the vacancies may be located according to a profilethat follows the expected excess deposition, as illustrated in FIG. 7B.FIG. 7B which is a cross section of the exemplary printed object of FIG.7A and a graph (a grey line) of an exemplary profile that matches thesurface curvature of the printed object. Equation (1) is a function ofthe graph the follows the profile of the cross section:

$\begin{matrix}{Y = {{A_{1}x^{n1}*e^{- \frac{x}{L_{1}}}} + {A_{2}/\left( {1 + \frac{x - x_{2}}{L_{2}}} \right)^{n2}}}} & (1)\end{matrix}$

Where: x is the distance from the edge of the printed region in thescanning direction, Y is the profile as a function of x and A₁, A₂, L₁,L₂, n₁, n₂ and x₂ are known constants. The amount of vacancies to beintroduced into the printing instructions may be according to afunction, such as the function of Equation (1).

In some embodiments, when the angle α (illustrated in FIG. 3B) is above70°, for example, between 70° and 90°, in order to further ensure thatno contact is made between a deposited support material layer and adeposited body material layer, a gap may be formed between regionsdeposited with the support material and those deposited with the modelmaterial. The gap may be a horizontal gap or an angular gap. In someembodiments, after depositing a predetermined number of layers or apredetermined high of deposited material, with a gap, the gap may beclosed by depositing additional support material or additional modelmaterial, such that at least some of the deposited layers extend beyondthe previously deposited layers, forming a negative angle.

Reference is now made to FIG. 8A illustrating an object printingaccording to known methods and further to FIG. 8B illustrating a 3Dobject according to some embodiments of the invention. As shown in FIG.8A there is no gap between body and support portions. An object 700 mayinclude a base portion 702, a substantially vertical portion 704 and atop portion 708. Portions 702, 704 and 708 may include a first material,for example, a body material. Portion 704 may not need to be verticaland may include at least one wall having an angle, for example, 1-30°,with respect to base portion 702. Object 700 may further include portion706 that includes a second material, for example, a support material. Insome embodiments, portions 702, 704 and 708 may include a supportmaterial and portion 706 may include a model material.

Portions 704 and 706 may be printed simultaneously layer by layer suchthat no gap is formed between the portions. In some embodiments, thequality of the interface between portions 704 and 706 may be of a lowquality, since both the first material and the second material aredeposited simultaneously in a single layer, forming a mixed interface.In order to avoid such a mixed interface, a gap may be formed betweenthe portions. An example of an object printed such that a gap is formedbetween the support material and the body materials is given in FIG. 8B.

An Object 720 may include a base portion 722 and a portion 724 having atleast one substantially vertical wall 725. In some embodiments, wall 725may have an angle, for example, 1-30°, with respect to the upper surfaceof base portion 722. Object 720 may further include top portion 728.Portions 722, 724 and 728 may include a first material, for example, amodel material. Object 720 may further include, a portion 726 having atleast one substantially horizontal wall 727 and a portion 736 depositedon top of portions 726. In some embodiments, wall 727 may have an angle,for example, 1-30°, with respect to the upper surface of base portion722. Portions 724 and 726 may be printed or deposited layer by layersuch that a gap 730 is formed between wall 725 and wall 727. The gap mayhave a width of at least 100 μm, for example, between 200 μm-500 μm.Examples of the influence of the width of the gap on the surface qualityare shown in the images of FIG. 10 , discussed below. Portion 736deposited on top of portion 726, such that gap 730 is gradually closedby depositing the second material at a negative angle 737. Negativeangle 737 may be of at least 1°, for example, between 5° and 25°.

Reference is now made to FIG. 9 , showing images of objects made ofsupport material printed at various negative angles, according to someembodiments of the invention. Eight pairs, each having a substantiallyvertical portion and a portion having a negative angle are shown. Eachpair was deposited such that a gap form between the two portions formingthe pair is potentially closed when the portions having negative anglesare deposited. For each pair negative angle is written below therespective image. It can be seen that up to 12.5°, the gap is wellclosed by a solid construction. Depositing a portion having a negativeangle larger than 25° caused a partial clash of the portion, while thegap remains open.

Objects 700 and 720 may be printed or deposited using an inkjet printingsystem, such as system 10 of FIG. 1 . Object 720 may be printed bydepositing on a substrate at least two different materials, for example,a body material and a support material. A first portion, e.g., portion724, may be deposited from a first material layer by layer and a secondportion, e.g., portion 726, may be deposited from a second material,layer by layer, such that a gap (e.g., gap 730) may be formed between asurface of the first portion (e.g., wall 725) and a surface of thesecond portion (e.g., wall 727). In some embodiments, the layers of thefirst and second portions may be deposited simultaneously, such that ata single deposition scan both a layer of the first portion and a layerof the second portion are deposited at substantially the same height.The gap may be larger than 200 μm.

After a predetermined number of layers of the first and second portions,the gap may be closed by printing a third portion (e.g., portion 736)from the second material on top of the second portion (e.g., portion726) layer by layer such that at least some of the deposited layersextend beyond the surface of the second portion (e.g., wall 727)(towards the surface of the first portion (e.g., wall 725)) to form anegative angle in the third portion. The negative angle may be higherthan 1°, for example, higher than 5°. In some embodiments, the firstportion may further be deposited layer by layer simultaneously to thedeposition of the third portion, at least until the gap is closed.

In some embodiments, the size of the negative angle may be determinedbased on the viscosity of the second material during the deposition. Thehigher the viscosity of the second material, the larger the negativeangle may be. In some embodiments, the size of the negative angle may bedetermined based on a surface tension of a droplet of the secondmaterial. The higher the surface tension, the higher the negative anglemay be. In some embodiments, the size of the negative angle may bedetermined based on the velocity of the droplets of the second materialduring deposition.

In some embodiments, the second and third portions (e.g., portions 726and 736) may be removed from the object to form the final model.

Results of experimental depositions of support and body material suchthat a gap is formed between the support and body material is presentedin FIG. 10 . FIG. 10 includes images of exemplary printed objectsaccording to some embodiments of the invention. Objects 910-960 wereprinted using a body material to form an internal bar and a supportmaterial to cover the vertical walls of each bar. An object 910 wasprinted such no gap is formed between the support and the modelmaterial, as illustrated for example, in FIG. 8A. Objects 920 and 930were printed with narrow gaps of, 80 μm and 160 μm respectively, betweenthe support and body portions of objects 920 and 930. In objects 910-930is was impossible to remove the support material and have smooth,glossy, high quality surface of the body bars. Objects 940, 950 and 960were printed such that gaps of 250 μm, 350 μm and 430 μm respectively,were formed between the body and the support portions of the objects. Ascan be see, smooth, glossy, high quality surfaces of the body materialbar was obtained.

In some embodiments, after completing the third portion of the objecthaving the negative angle, an additional material may be deposited toform a buffer zone. FIGS. 11A and 11B illustrate two exemplary printedobjects according to some embodiments of the invention. Objects 1010 and1020 may include body portions 1012 and 1022, gaps 1015 and 1025 andsupport portions 1017 and 1027, respectively. Gaps 1015 and 1025 mayhave negative angles according to embodiments of the invention. Gaps1015 and 1025 may be closed by printing buffer zones in the contactbetween the body portions and the support portions. Object 1010 mayinclude a straight buffer zone 1013 and object 1020 may include anangular buffer zone 1023. Buffer zones 1013 and 1023 are given asexamples only. Buffer zones according to the invention may have anydesirable geometry.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

The invention claimed is:
 1. A system for printing a three-dimensional(3D) object and a support construction for the 3D object, comprising: aprinting unit comprising one or more print heads configured to depositbody material for forming the 3D object and support material for formingthe support construction; a supply system for supplying the bodymaterial and support material to the printing unit; and a controllerconfigured to: generate 3D cross sectional digital data comprising a setof horizontal slices, wherein each of the slices includes one or morebody regions representing a horizontal cross section of the 3D object,and at least each of some of the slices further includes one or moresupport regions being adjacent to the body region and representing acorresponding horizontal cross section of the support construction;manipulate the 3D digital data to create a set of shifted slices byperforming vertical shifts between the body region and the supportregion of a same horizontal slice to create printing digital data,wherein at least each of some of the shifted slices includes a bodyregion of one of the horizontal slices together with a support region ofanother one of the horizontal slices; and control the printing unit todeposit, in layers, from the one or more printing heads, the bodymaterial and the support material based on the printing digital data,wherein in a single scan, droplets of the support material and dropletsof the body material travel different distances.
 2. The system of claim1, wherein the controller is further configured to control the printingunit to simultaneously deposit a region of the 3D object related to aparticular horizontal cross section together with a region of thesupport construction related to a different horizontal cross sectionlayer.
 3. The system of claim 1, wherein the controller is furtherconfigured to: determine a height of the vertical shift between the bodyregion and the support region based on a geometrical relationshipbetween the 3D object and the support construction.
 4. The system ofclaim 3, wherein the geometrical relationship is an angle formed betweena surface representing the interface between the body region and thesupport region and horizon.
 5. The system of claim 4, wherein a higherangle requires a higher vertical shift.
 6. The system of claim 1,wherein the 3D cross sectional digital data further comprises a set ofvertical columns, wherein each of the columns includes one or moreslices of body regions representing a vertical column of the 3D object,and at least each of some of the columns further includes one or moreslices of support regions being vertically adjacent to the body regionand representing a corresponding vertical column of the supportconstruction, and wherein manipulating the 3D digital data furtherincludes adding to each column a delay in the printing process betweenevery vertically adjacent body region and support region.
 7. The systemof claim 1, wherein: the printing unit further includes one or morehardening devices, and wherein the controller is further configured tocontrol the one or more hardening devices to harden the deposited bodymaterial and support material deposited after each scan.
 8. The systemof claim 1, wherein each slice includes two or more deposition layers.9. The system of claim 1, wherein manipulating the 3D digital datafurther comprises creating vacancies in at least some of the slices suchthat after depositing all the layers both the 3D object and the supportstructure are at the same height, wherein in each vacancy no supportmaterial or body material is dropped.
 10. The system of claim 1, furthercomprising: a fabrication platform for carrying the printed material.